The proposed research program seeks to detail the geometry of complexes of carcinogenic polycyclic hydrocarbons with DNA and chromatin and to elucidate the intermolecular interactions which stablize them. Our approach will be through the utilization of magnetic properties in the excited triplet states of the carcinogen to probe the orientations and interactions within the complex, using newly developed methods of optical detection of magnetic resonance. Our experiments will focus on complexes of nucleic acids with polycyclic hydrocarbons which have been postulated to be actively involved in carcinogenesis and which may be of importance in elaborating mechanisms of chemical carcinogenic activity at the molecular level.